\xiti\mylabel{xiti-11}

\begin{xiaotis}

\xiaoti{利用矩阵的行的初等变换，把下列矩阵化为主对角线下方的元素全部为零的矩：}
\begin{xiaoxiaotis}

    \renewcommand\arraystretch{1.2}
    \begin{tabular}[t]{*{2}{@{}p{16em}}}
        \xiaoxiaoti{$\begin{pmatrix*}[r]
                2 & 2 & 3 \\
                4 & 1 & -1 \\
                4 & 1 & 3
            \end{pmatrix*}$；}
        & \xiaoxiaoti{$\begin{pmatrix*}[r]
                1 & 0 &  2 & 1 \\
                3 & 3 &  1 & 0 \\
                3 & 1 & -1 & 2 \\
                3 & 0 &  0 & 0
            \end{pmatrix*}$。}
    \end{tabular}

\end{xiaoxiaotis}


\xiaoti{用顺序消元法（矩阵表示）解方程组：}
\begin{xiaoxiaotis}

    \renewcommand\arraystretch{1.2}
    \begin{tabular}[t]{*{2}{@{}p{16em}}}
        \xiaoxiaoti{$\begin{cases}
                x + 2y + 3z = -1, \\
                3x + 5y - 2z = 9, \\
                2x - y + 4z = 5;
            \end{cases}$}
        & \xiaoxiaoti{$\begin{cases}
                2x - y + 2z = 8, \\
                2x + y - 6z = -2, \\
                3x + y - 4z = 1;
            \end{cases}$} \\[3em]
        \xiaoxiaoti{$\begin{cases}
                x + 2y + 2w = 4, \\
                x + y + 2z - w = -2, \\
                2x - y + z - w = -3, \\
                3x + 4y - z + 3w = 8;
            \end{cases}$}
        & \xiaoxiaoti{$\begin{cases}
                x - y - 2z + 2w = -3, \\
                2x - y + 3z + 2w = 6, \\
                x + y + 2z + 3w = 6, \\
                x - 3y - z - w = -2 \text{。}
            \end{cases}$}
    \end{tabular}

\end{xiaoxiaotis}

\end{xiaotis}

